This invention relates to a method of vaporizing molten alloys of metals of different vapor pressures from elongated vaporizing crucibles which are fed at several points distributed over their length with vaporizing material in rod form, by the direct bombardment of the bath surface with electron beams periodically deflected according to a pattern, and for the deposition of the alloy material onto a plurality of substrates which are arrayed in a field above the vaporizing crucible.
From a publication by Chromalloy American Corporation, New York, U.S.A., "High Temperature Resistant Coatings for Superalloy," by Seelig et al, it is known to coat gas turbine blades with oxidation- and corrosion-resistant coatings, for example of CoCrAlY and NiCoCrAlY. The coating or coatings on an individual bucket must be substantially homogeneous, i.e., they must not vary in composition from the beginning to the end of the deposition process. If the process is to be performed on a large technical scale, a plurality of blades must be coated simultaneously in a single deposition cycle. This requires large-area vaporization crucibles. The differences in thickness and composition must not depart from relatively narrow tolerances from one substrate to the next.
However, it is known that vapor deposition processes are subject to what are known as "margin effects," i.e., the thickness and composition of the coatings on the substrates situated at the margin of the vaporization crucible generally differ from those of the substrates situated in the center. To avoid a loss of coating thickness towards the margins, it is already known to increase the dwell time of an electron beam oscillating over the bath surface at both ends of the vaporizing crucible. However, the problem of different alloy compositions cannot be solved by this means alone.
From published German application No. 2,812,285, it is known to counteract the local variation of alloy compositions in the deposited coatings by bombarding the bath surface in the vaporizing crucible with one or more focused electron beams according to a particular pattern of displacement of the beam while maintaining particular dwell time ratios. The method of the invention provides a solution to the problem.